The study was carried out by Alexander Bigazzi, a single author from the University of British Columbia. No sources of funding were reported.

The article is currently available in manuscript form and is set to be published in the peer-reviewed International Journal of Sustainable Transportation.

The Sun and the Mail Online both inappropriately stated high-speed cyclists are at risk of lung cancer and stroke, which is certainly not proven by this study, nor the objective of the paper.

What kind of research was this?

This was a mathematical modelling study where Bigazzi aimed to derive equations to estimate the air pollution inhalation dose pedestrians and cyclists are exposed to when travelling at a particular speed.

Bigazzi explains how there is a balance with high-speed active travel – such as running or cycling – and exposure to pollution because of the trade-off between higher breathing rate (which increases exposure) against the shorter duration time (which decreases exposure).

This study applied exposure levels from the literature to an imaginary population of travellers to calculate individual minimum dose speed (MDS).

MDS is described as the speeds that minimise the air pollution inhalation dose per unit of distance travelled.

But as the study is all model-based, it can’t give concrete findings.

What did the research involve?

Bigazzi’s methods describe a complex series of mathematical equations that are not possible to explain in-depth here.

In summary, Bigazzi generated a series of equations to determine the steady state pollution dose a person inhales, depending on differing circumstances. He then aimed to determine the speed that would minimise these values.

He made several assumptions for the analysis, including that the pollution concentration cyclists or pedestrians are exposed to is independent of speed, and that breathing rate increases with speed.

Increasing speed was always determined to reduce inhalation dose over a fixed distance. He then calculated breathing rate as a function of speed for cyclists and pedestrians.

He finally calculated MDS for a range of travellers. The author used population distributions from the 2012 US census to imagine a theoretical population of 10,000 people of a range of ages, half male and half female.

For these people he used functions of age, sex and body mass to calculate their resting metabolic rate and oxygen consumption.

He also inputted data on work/power rate during cycling from the American College of Sports Medicine, and additional factors like bicycle mass, road grade and resistance, air density and drag. This was also done for walking and jogging.

What were the basic results?

As the author says, the minimum dose speed (MDS) – the speed that minimises the air pollution inhalation dose – is “within a range of reasonable pedestrian and bicycle speeds”.

The MDS was calculated to be:

3-8km an hour for walking

8-13km an hour for jogging on flat ground

12-20km hour for cycling on flat ground

Energy expenditure and breathing rate increase with increasing road grade for both cyclists and pedestrians, which decreases the MDS.

However, it has a greater impact on cyclists because of the higher speeds they travel at and the extra weight of the bike.

Each 1% increase in road grade decreases MDS for cyclists by up to 1.6km an hour, depending on the equation model used.

Large deviations from the MDS – for example, more than 10km an hour for cyclists – was calculated to more than double the pollution inhalation dose over a fixed distance.

Some cyclists now choose to wear a face mask to protect against air pollution. If you decide to buy one, it’s recommended you get one that contains sub-micron filters, as this will help protect against the most dangerous types of pollution particles.